Question

Ethanol, C2H6O, is most often blended with gasoline - usually as a 10 per cent mix - to create a fuel called gasohol. Ethanol is a renewable resource and ethanol-blended fuels, like gasohol, appear to burn more efficiently in combustion engines. The heat of combustion of ethanol is 326.7 kcal/mol.
The heat of combustion of 2-methylheptane, C8H18, is 1.306×103 kcal/mol. How much energy is released during the complete combustion of 394 grams of 2-methylheptane ?
_______kcal
Assuming the same efficiency, would 394 grams of ethanol provide more, less, or the same amount of energy as 394 grams of 2-methylheptane?
_________
A. more or
B. less or
C. the same amount

Answer 1

Answer:

4.51 × 10³ kcal

B. less

Explanation:

Let's consider the combustion of 2-methylheptane.

C₈H₁₈ + 12.5 O₂ ⇒  8 CO₂ + 9 H₂O

When 1 mole of C₈H₁₈ burns, 1.306 × 10³ Kcal are released (heat of combustion). The molar mass of C₈H₁₈ is 114 g/mol. Then, for 394 g of C₈H₁₈:

$394gC_{8}H_{18}.\frac{1molC_{8}H_{18}}{114gC_{8}H_{18}}.\frac{1.306 \times 10^{3} kcal }{1molC_{8}H_{18}} =4.51 \times 10^{3} kcal$

Assuming the same efficiency, would 394 grams of ethanol provide more, less, or the same amount of energy as 394 grams of 2-methylheptane?

Let's consider the combustion of ethanol.

C₂H₆O + 3 O₂ ⇒  2 CO₂ + 3 H₂O

When 1 mole of C₂H₆O burns, 326.7 Kcal are released (heat of combustion). The molar mass of C₂H₆O is 46.0 g/mol. Then, for 394 g of C₂H₆O:

$394gC_{2}H_{6}O.\frac{1molC_{2}H_{6}O}{46.0gC_{2}H_{6}O}.\frac{326.7 kcal }{1molC_{2}H_{6}O} =2.80 \times 10^{3} kcal$

The combustion of 394 g of ethanol provides less energy than the combustion of 394 g of 2-methylheptane.

Answer 2

Answer: the answer is B. less

Explanation:

hope this helps :D